Solvent Mediated Superexchange in a C-Clamp Shaped Donor-Bridge-Acceptor Molecule: The Correlation between Solvent Electron Affinity and Electronic Coupling

摘要

The temperature dependence of intramolecular electron-transfer rate constants for a C-shaped donor-bridge-acceptor molecule was measured in a series of solvents of differing electron affinities. The rate data was analyzed using a semiclassical version of the Marcus equation. The reaction free energies were characterized using a molecular model for solvation. The electronic coupling between the electron donor and acceptor groups is enhanced in solvents with more positive electron affinity. This enhancement arises from solvent occupation of a cleft between the donor and acceptor groups, resulting in an increase of the electronic coupling via an enhancement of the superexchange interaction. Solvents with more positive electron affinity provide mediating, superexchange states whose energies are closer to that of the resonant, initial, and final states.